Continental Crust

Continental crust is the granitic to granodioritic outer layer that forms the continents and their submerged margins. It averages about 35 km thick and reaches 50 to 70 km under young mountain belts, far thicker than the roughly 7 km of oceanic crust. Its mean density near 2.7 g/cm3 is lower than oceanic crust near 2.9 g/cm3, so it rides higher by isostasy and resists subduction; this is why continental crust survives for billions of years while ocean floor recycles within about 200 million years. It carries the oldest rocks on Earth, over 4 billion years in the Canadian and Australian cratons.